1. Field of the Invention
The invention relates generally to the field of photolithographic technologies used in electronic fabrications processes.
More specifically, the invention relates to a method for defining an electrically conductive metal structure on a three-dimensional element which, in one embodiment, may comprise defining an electrically conductive metallic trace, pattern, electrode or other structure on the surface of a glass microsphere or spherical shell resonator.
The invention further relates to a device made from the method of the invention.
2. Description of the Related Art
Three-dimensional micro-machined structures comprising spherical, semi-spherical or hemi-spherical glass structures have application in signal processing, frequency and timing control and inertial measurement. An example of prior art glass structures, which are referred to as “shell resonators” in literature, is found in “3D Micromachined Spherical Shell Resonators With Integrated Electromagnetic and Electrostatic Transducers”, Zotov et al., Solid State Sensors, Actuators and Microsystems Workshop (Jun. 6-10, 2010), the entirely of which is incorporated herein by reference.
The dimensions of a glass shell resonator structure may be quite small, in the range of 1 mm diameter or less, and the shell material may be comprised of a glass material such as Corning Pyrex 7740 that is formed using a wafer-scale glassblowing process. A prior art process for fabricating glass shell resonator structures is disclosed in “Method and Apparatus of Wafer-Level Micro-Glass-Blowing), U.S. Pat. No. 7,694,531 to Eklund, et al., the entirety of which is incorporated herein by reference.
In one application, glass shell resonator structures having electrically conductive metal traces or structures disposed on the surfaces thereof, oscillate in a vibratory mode at resonance by means of an excitation frequency. Depending on the sensor application of the resonators, changes in resistance, magnetic characteristics, capacitance or other physical characteristic of the trace, traces or between adjacent traces on adjacent shell resonator structures are measured and used to sense acceleration, frequency change, temperature change, rotation and the like.
Because shell resonator structures have relatively small feature sizes and radial and non-planar surfaces, defining the electrical conductive metal traces or electrodes on the surface of the structure is challenging.
Prior art attempts include defining metal traces on a flat glass layer in a Pyrex-Si wafer stack prior to forming the resonator structures in a high temperature thermal process but difficulty in devising a metal stack with sufficient ductility to permit plastic deformation concurrent with the formation of the glass shell structure requires complex, costly, multiple plating steps, each of which introduces a potential for lower yields.
What is needed is a method for providing metal traces or structures on a three-dimensional structure such as a shell resonator structure that is reliable, precise and relatively simple.